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# AUParameterObserver

A block called after the value of a parameter changes.

```
typealias AUParameterObserver = (AUParameterAddress, AUValue) -> Void
```

## Discussion

The block takes the following parameters:

- address: The address of the parameter.
- value: The current value of the parameter.

## See Also

[`-  tokenByAddingParameterObserver:`](/documentation/AudioToolbox/AUParameterNode/token(byAddingParameterObserver:))

Adds an observer for a single parameter or all parameters in a group.


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